From f5cf131a9d8984bd6b3403396beed2ffbc26bded Mon Sep 17 00:00:00 2001
From: Chris Wilson <chris@chris-wilson.co.uk>
Date: Tue, 27 Apr 2010 18:56:23 +0100
Subject: [PATCH] surface: skip OVER is the source is clear.

If the source has no alpha, the OVER operation becomes DST, i.e. a
no-op.
---
 src/cairo-surface.c | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/src/cairo-surface.c b/src/cairo-surface.c
index 8a5937349..ddb1ffd8b 100644
--- a/src/cairo-surface.c
+++ b/src/cairo-surface.c
@@ -1926,6 +1926,12 @@ _cairo_surface_paint (cairo_surface_t	*surface,
     if (op == CAIRO_OPERATOR_CLEAR && surface->is_clear)
 	return CAIRO_STATUS_SUCCESS;
 
+    if (op == CAIRO_OPERATOR_OVER &&
+	_cairo_pattern_is_clear (source))
+    {
+	return CAIRO_STATUS_SUCCESS;
+    }
+
     status = _pattern_has_error (source);
     if (unlikely (status))
 	return status;
@@ -1971,6 +1977,12 @@ _cairo_surface_mask (cairo_surface_t		*surface,
 	return CAIRO_STATUS_SUCCESS;
     }
 
+    if (op == CAIRO_OPERATOR_OVER &&
+	_cairo_pattern_is_clear (source))
+    {
+	return CAIRO_STATUS_SUCCESS;
+    }
+
     status = _pattern_has_error (source);
     if (unlikely (status))
 	return status;
@@ -2097,6 +2109,12 @@ _cairo_surface_stroke (cairo_surface_t		*surface,
     if (op == CAIRO_OPERATOR_CLEAR && surface->is_clear)
 	return CAIRO_STATUS_SUCCESS;
 
+    if (op == CAIRO_OPERATOR_OVER &&
+	_cairo_pattern_is_clear (source))
+    {
+	return CAIRO_STATUS_SUCCESS;
+    }
+
     status = _pattern_has_error (source);
     if (unlikely (status))
 	return status;
@@ -2147,6 +2165,12 @@ _cairo_surface_fill (cairo_surface_t	*surface,
     if (op == CAIRO_OPERATOR_CLEAR && surface->is_clear)
 	return CAIRO_STATUS_SUCCESS;
 
+    if (op == CAIRO_OPERATOR_OVER &&
+	_cairo_pattern_is_clear (source))
+    {
+	return CAIRO_STATUS_SUCCESS;
+    }
+
     status = _pattern_has_error (source);
     if (unlikely (status))
 	return status;